Feb 25, 2000

The Effects of a Bottleneck on Inbreeding Depression and the Genetic Load

The American Naturalist
Mark Kirkpatrick, Philippe Jarne


We study the effects of a population bottleneck on the inbreeding depression and genetic load caused by deleterious mutations in an outcrossing population. The calculations assume that loci have multiplicative fitness effects and that linkage disequilibrium is negligible. Inbreeding depression decreases immediately after a sudden reduction of population size, but the drop is at most only several percentage points, even for severe bottlenecks. Highly recessive mutations experience a purging process that causes inbreeding depression to decline for a number of additional generations. On the basis of available parameter estimates, the absolute fall in inbreeding depression may often be only a few percentage points for bottlenecks of 10 or more individuals. With a very high lethal mutation rate and a very slow population growth, however, the decline may be on the order of 25%. We examine when purging might favor a switch from outbreeding to selfing and find it occurs only under very limited conditions unless population growth is very slow. In contrast to inbreeding depression, a bottleneck causes an immediate increase in the genetic load. Purging causes the load to decline and then overshoot its equilibrium value. The changes are ty...Continue Reading

Mentioned in this Paper

Dysequilibrium Syndrome
Genetic Linkage
Mutation Abnormality

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